Tick Mark

A tick mark is a short line placed at regular intervals along a chart axis to indicate a specific value and to anchor the label that names it.

An axis line on its own is just a stripe; it does not tell you where "20" sits versus "40." Tick marks solve this by dividing the line into measured steps. Each tick is a reference point: the place where a particular value lives. The numbers or category names you read next to an axis are positioned at these ticks, which is why ticks and labels almost always appear together.

How tick marks work in a chart

Ticks usually fall at evenly spaced intervals chosen to be easy to read — every 10, every 25, every 100. Many charts distinguish major ticks (longer, labelled, often with a gridline) from minor ticks (shorter, unlabelled) that subdivide the gaps for finer reading. The spacing between ticks is set by the axis scale: on a linear scale the gaps represent equal value differences, so equal pixel spacing means equal numeric steps.

A concrete example

Take a vertical axis running from 0 to 100. If major ticks are placed every 25, you get marks at 0, 25, 50, 75 and 100 — five evenly spaced ticks. A bar whose top lands exactly halfway between the 50 tick and the 75 tick represents a value of about 62 or 63, because halfway between 50 and 75 is 62.5. Without those ticks you could not estimate the height at all; with them you can read it to within a couple of units.

Related terms

Tick marks sit on an axis and are positioned by its scale; faint gridlines often extend from major ticks across the plot to make values easier to trace. See ticks at work in the bar chart guide.